1. Field of the Invention
The present invention relates to a temperature compensation circuit.
2. Background Art
In a wireless communication device, particularly in a power amplifier for a transmission system (a high-frequency power amplifier), temperature compensation is required.
In general, when a temperature characteristic with respect to a gain of a common-emitter amplifier is desired to be flattened, a current flowing in the amplifier is provided with a temperature characteristic proportional to absolute temperature. Such current is called a PTAT (Proportional To Absolute Temperature) current. Theoretically, it is considered that the temperature characteristic of the gain is thereby to be flattened. For this reason, this method is frequently used in the common-emitter amplifier as a temperature compensation method.
However, in a high frequency signal, the temperature characteristic of the amplifier lowers the gain at a high temperature actually. The lowering of the gain is considered to result from various factors such as Ft (cutoff frequency) of a transistor and increase in resistance of metal. For this reason, conventionally, temperature compensation for the gain at a high temperature has been insufficient.
According to a technique disclosed in JP 2006-191482, the lowering of the gain at a high temperature is prevented by clamping a signal line by a diode to regulate a current flowing through the diode. However, this is not suited for a high-frequency processing circuit because a large loss is brought about in the diode. For this reason, even this conventional art cannot prevent the lowering of the gain at a high temperature.